I've given and received oral sex with a woman. A few weeks after I developed a sore throat that went away with antibiotics. After taking the antibiotics, I developed red spots on the roof of my mouth that went away within a week. I am now worried sick that I might have gotten HIV from her. These thoughts keep running through my mind. I know there is a small risk of getting it from oral sex, but after those symptoms I have been very uneasy. Can someone reassure me here?

I may be no expert, but I don't think that HIV shows signs that quickly. I think that you should stop worrying and take things as they come. Even though you're probally at low risk, get tested in a few weeks (three months after the encounter) Hopefully everything will work out okay. :)

I waited 3 very long months and got tested. It was negative!! Should I finally put this worrying to rest? I heard sometimes you might have to get tested again... Please advise.

Yes, if you tested after 3 months, like you say you did, you are conclusively negative.

The risk of acquiring HIV from oral sex is exceedingly rare, combined with the chance of seroconverting (changing from - to +) after your 3 month test is exceedingly low, you are 100% negative.

The only reason a person would be advised to go back for a 6 month HIV test is if they are on chemotherapy, or organ anti-rejection medication.